1. Field
The invention disclosed and claimed herein generally pertains to a method for reducing multipath signal degradation effects which occur at the receiver of a wireless transmission system. More particularly, the invention pertains to a method of the above type wherein the multipath degradation effects are caused by a moving signal-reflective vehicle, such as an aircraft or other object, which passes through the signal transmission path. Even more particularly, the invention pertains to a method of the above type wherein multipath signal degradation is reduced by determining the specific position of the moving aircraft or other reflective vehicle, with respect to components of the wireless transmission system.
2. Description of the Related Art
Ghosting, or the occurrence of ghosts in a displayed television or video image, is a well known example of multipath distortion or degradation that can affect reception of transmitted signals. Typically, one component of a transmitted television signal travels directly from the transmitter to a television receiver, to produce a primary image at the receiver. Another signal component travels toward a signal reflective structure, such as a building or the like, or toward a moving structure or object, such as an aircraft, and is reflected thereby to the receiver. Since the reflected component travels over a longer path than the direct component, the reflected component experiences a slight time delay in reaching the television receiver, with respect to the direct component. The reflected component produces a secondary image, which is generally fainter than the primary image, and is offset positionally from the primary image.
As is well known by those of skill in the art, ghosting is a phenomenon associated with analog television. However, multipath degradation of the above type can also affect digital television transmissions. More particularly, reception of both direct and reflected components of the same digital signal can cause bit framing errors. These errors result in audio distortions and loss of picture quality.
Aircraft and other moving vehicles or objects raise special issues in regard to multipath signal degradation, in that their positions are not fixed with respect to the signal transmission system transmitter or receiver. Also, the travel or entry of such moving vehicles into regions of wireless signal transmission, resulting in multipath effects as described above, will frequently be unknown or unpredictable. At present, however, techniques used to remove the effects of secondary signal reception, caused by moving aircraft or the like, generally require extensive and sophisticated signal processing operations. Such techniques are supported by circuit designs and processing logic that is usually characterized by a high degree of complexity.